Loss of visual acuity is a growing concern worldwide. The World Health Organization currently estimates to 2.5% the incidence of low vision in industrialized countries and this figure is expected to continue increasing with ageing population. Low vision may be generally referred to as a condition where ordinary eye glasses, lens implants or contact lenses are not sufficient for providing sharp sight. The largest growing segment of the low-vision population in developed countries is expected to be people aged 65 years old and older, which most notably due to age-related eye diseases such as macular degeneration, glaucoma and diabetic retinopathy, cataract, detached retina, and retinitis pigmentosa. Some people are also born with low vision.
Low-vision individuals often find it difficult, if not impossible, to read small writing or to discern small objects without high levels of magnification. This limits their ability to lead an independent life because reading glasses and magnifying glass typically cannot provide sufficient magnification for them. In order to assist low-vision individuals in performing daily tasks, various magnification devices and systems are known in the art and may be broadly classified into one of two categories: desktop and portable video magnifiers.
On the one hand, desktop video magnifiers generally include a video monitor mounted on a stand having a gooseneck shape. A camera having a large optical zoom is installed on the stand over a working area on which a user disposes an object to be magnified, which is typically a document the user wishes to read. The camera feeds a video processor with a video signal of the working area, and the video processor in turn feeds this video signal with an increased sharpness and enhanced contrast to the video monitor. The document is typically disposed on an XY translation table assembled on rails, allowing the user to freely move the XY table and the document thereon to bring different portions of the document within the field of view of the camera.
On the other hand, portable or handheld video magnifiers are devices that are small enough to be easily carried by a user in a pocket or purse. Such devices may typically include a video camera on one side and a small built-in LCD display on the other side. Portable video magnifiers typically include a video processor providing sharpness enhancement, enhanced contrast modes and digital magnification. More particularly, while appropriate for use in many applications, currently available handheld magnification devices suffer from a number of limitations. One limitation is that known handheld magnification devices have a limited depth of field in that they are generally capable of magnifying close objects with acceptable video images sharpness, but are typically not adapted for providing high-quality video images over a broad and continuous range of working distances.
In view of the above considerations, there is therefore a need in the art for a handheld magnification device directed to low-vision individuals that alleviates at least some of the drawbacks of the prior art.